In processing speech and audio signals, pitch detection is one of key technologies in various actual speech and audio applications. For example, the pitch detection is the key technology in applications of speech encoding, speech recognition, karaoke, and the like. Pitch detection technologies are widely applied to various electronic devices, such as, a mobile phone, a wireless apparatus, a personal digital assistant (PDA), a handheld or portable computer, a global positioning system (GPS) receiver/navigator, a camera, an audio/video player, a video camera, a video recorder, and a surveillance device. Therefore, accuracy and detection efficiency of the pitch detection directly affect the effect of various actual speech and audio applications.
Current pitch detection is basically performed in a time domain, and generally, a pitch detection algorithm is a time domain autocorrelation method. However, in actual applications, pitch detection performed in the time domain often leads to a frequency multiplication phenomenon, and it is hard to desirably solve the frequency multiplication phenomenon in the time domain, because large autocorrelation coefficients are obtained both for a real pitch period and a multiplied frequency of the real pitch period, and in addition, in a case with background noise, an initial pitch period obtained by open-loop detection in the time domain may also be inaccurate. Here, a real pitch period is an actual pitch period in speech, that is, a correct pitch period. A pitch period refers to a minimum repeatable time interval in speech.
Detecting an initial pitch period in a time domain is used as an example. Most speech encoding standards of the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) require pitch detection to be performed, but almost all of the pitch detection is performed in a same domain (a time domain or a frequency domain). For example, an open-loop pitch detection method performed only in a perceptual weighted domain is applied in the speech encoding standard G729.
In this open-loop pitch detection method, after an initial pitch period is obtained by open-loop detection in the time domain, correctness of the initial pitch period is not performed, but close-loop fine detection is directly performed on the initial pitch period. The close-loop fine detection is performed in a period interval including the initial pitch period obtained by the open-loop detection, so that if the initial pitch period obtained by the open-loop detection is incorrect, a pitch period obtained by the final close-loop fine detection is also incorrect. In other words, because it is extremely hard to ensure that the initial pitch period obtained by the open-loop detection in the time domain is absolutely correct, if an incorrect initial pitch period is applied to the following processing, final audio quality may deteriorate.
In addition, in the prior art, it is also proposed to change the pitch period detection performed in the time domain to pitch period fine detection performed in the frequency domain, but the pitch period fine detection performed in the frequency domain is extremely complex. In the fine detection, further pitch detection may be performed on an input signal in the time domain or the frequency domain according to the initial pitch period, including short-pitch detection, fractional pitch detection, or multiplied frequency pitch detection.